Compressor unloader



Patented May 1, 1951 U N IT ED STATE S TENT OFFICE ApplicationJune 8, 1948, Serial No. 31,718

This invention relates to compressors and compressor unloaders, and more particularly to an unloader system for multi-stage compressors.

In the present invention complete unloading of the compressor is facilitated by exhausting the cylinders of the high pressure stages through the intercoolers to the/initial or low pressure stage and thence, as is that stage, from the outlet to the inlet or suction side of the Vlow pressure stage. In this manner any external piping, used heretofore to carry the exhaust to a point remote from the compressor to avoid the noise and other general annoyances associated with unloading, is eliminated, thereby materially reducing the original and upkeep cost of the compressor uploader system.

It is accordingly one object of my invention to unload a compressor by reversing the normal direction of now of pressure ui'd in the system.

` Other objects will be in part obvious and in part pointed out hereinafter.

In the drawings accompanying this 'speciiication and in which similar' reference numerals refer to similar parts,

' Figure 1 is an end view, partly in section, of a variable capacity-multi. stage` compressor embodying the present invention,

Figures 2 and 3 are transverse views taken through Figure 1 along the lines 2---2v and 3 3, respectively,

Figure 4 is a transverse view vtaken through Figure 2 along the line 4--4 and showsa construction of a by-pass valve for the high pres'- svure stage of the compressor, and- Figure 5 is an end view of the 'by-pass valves for the high pressure stage of the compressor.

Referring more particularly to the drawings, number I@ designates, in general, a variable capacity-multi stage compressor provided with clearance control valves II, the action of which are controlled by a pressure responsive regulating device I2 that receives its supply of pressure iiuid from a source (not shown) .by means of a branch on the conduit I 3 that supplies pressure fluid to operate the by-passvalves I4 and I5 on the high and low pressure stages It and I1, respectively, of the compressor. The by-pass valves I4 and I5 serve as a means whereby the vcompressor may be completely unloaded byV reversing the normal direction of flow of pressure iiuid through the compressor system, i. e. any pressure fluid in the high pressure stage I6 is Icy-passed through the intercooler I3 connected between the two stages and thence throughl the low pressure stage Il' to the inlet or suction sideV I9 thereof..

For the sakeof simplicity the multi-stagecompresser is shown as being of two stage type and each stage has a casing or cylinder 2li which forms the compression chamber 2I for the recip- 5 Claims. (Cl. 230-26) rocatory piston 22. As shown, the compressor is of the double acting type and is, accordingly, provided with inlet and discharge valves 23 and 24, respectively, in the outer periphery of the opposite end portions of the cylinder 2l), and the ends and the 'intermediate portion of the cylinder 2i! is provided with water jackets 25.

Encircling each of the cylinders 2Q is a housing 26 that cooperates with the cylinder 2!) to form a chamber which is sub-divided by the radially extended rib mem-bers 2l and 3l that, respectively, encircle and extend longitudinally of the cylinder 2li, to form clearance pockets 28 and inlet and outlet passages 29 and 3U, respectively, for the compressor. In the low pressure stage an additional support member 3i extends par tially around the cylinder 20 and cooperates with the member 2i and the housing 2S to form ay by-pass passage 32 that communicates the inlet and outlet of that stage. In this instance there' are two clearance pockets 28 positioned at each end of the cylinders 2li, which are communicated with the compression chamber 2| by the ports 33, in the cylinder 28, through which the iiow of pressure fluid is controlled by the clearance valves II mounted in the housing 2S. With this arrangement a step-by-step unloading of the compressor in one-quarter capacity steps is available and in order to accomplish complete unloading, one clearance pocket at each end of the housing 26 of the high pressure stage I6 is communicated with the inlet passage 29 through openings 34 in the support member :i1-thus, this arrangement in cooperation with the passage 32, provides a ow path for reverse flow from the high pressure cylinder to the inlet side of the low pressure cylinder.

In order that positive control can be exercised over the complete unloading of the compressor, means are provided for controlling the communication between the clearance pockets 28 and the inlet 29 of the high pressure stage I6 and to this end, the fluid pressure operated valves I t are mounted in the housing 2@ of the high pressure stage to control the flow of pressure fluid through the openings 3ft. As shown, the

' valves It are oi the piston type, and are held in the closed position by pressure fluid delivered thereto through the conduit I3, and held in the open position by means of springs '38.

In this manner the opposite ends of the compression chamber ZI in the high pressure stage are communicated with the inlet 29 whenever the valves Id and the clearance valve II in the associated clearance chambers, are in the open position. The valve I5, which operates in a somewhat similar manner to the valves Ill, is mounted in the housing of the low pressure stage I 'I and serves as a means for controlling the flow of air through an opening 35 in the member 39 positioned across the passage 32. The valve I5, so positioned, effectively controls communication between-the inlet and outlet of the low pressure stage.

In order that the by-pass valves I4 and I5 and the regulator I2 may be operated simultaneously, a three way control valve 38 is connected in the conduit I3; thus pressure fluid is supplied to and exhausted from the by-pass valves and the regulator, and therefore the clearance valves I I, by merely changing the control position of the valve 38. With this arrangement the valves I4 and I5 operate in a timed relation and in so doing permit the escape of pressure uid from the compression chamber 2l in the high pressure stage I6 through the intercooler I8 connected in series with the preceding stage-that is, connected between the outlet 3l] of the low pressure stage and the inlet 29 of the high pressure stage, and thence the fluid passes through the passage 32 in the low pressure stage to the inlet or suction side I9 thereof. The valve 38 may, or" course, be regulated automatically, but for the sake of simplicity it is shown as being of the manually operated type. In one position, the control valve 38 permits the flow of pressure iluid to the regulator I2 and the by-pass valves I4 and I5 so that the valves Ill and I5 are held in the closed position and the regulator i2 controls the operation of the clearance control valves II in a well known manner. In the second position of the valve 38, pressure fluid is exhausted from that portion of the conduit I3 which extends beyond the valve 38 and thus the springs 35 bias the valves I4 and I5 into the open position and the source of pressure fluid for actuating the regulator I2 is cut-ofi" and the clearance valves Il are therefore also biased into the open position. The compressor is then completely unloaded. In the third position of the control valve 38, the low of pressure fluid through the conduit I3 is halted.

In operation, assuming the control valve is in the rst position described, the compressor operates in a well known manner with the regulator I 2 automatically controlling the operation of the clearance valves II so that a constant pressure is maintained in that portion (not shown) of the fluid circuit to which the regulator E2 is connected. In the event the operator desires to completely unload the compressor, it is mereiy necessary to move the valve 38 into the second mentioned position and thus pressure uid is exhausted from the by-pass valves I and I5 and the regulator I2. In this position of the valve 38, the clearance control valves i I and the by-pass valves It and I5 are in the open position, and the high and low pressure cylinders 2B are communicated with the inlet or suction side IS of the low pressure stage. That is, any pressure iiuid in the high pressure cylinder may escape into clearance pockets 28, through the opening 35, into the inlet of the high pressure stage and thence through the intercooler I8 to the outlet of the low pressure stage and around the low pressure cylinder through the passage 32 to the atmosphere.

It is now obvious that the present invention provides a simple and eiective means for completely unloading a compressor, which is highly important in starting and stopping the unit. By relieving the pressure on the compressor cylinders when starting up the unit, the prime mover, such as a synchronous motor, may come up to Operating or synchronous speed under reduced torque. In the event the prime mover is shut down simultaneously with the unloading of the compressor, complete unloading prevents whipping of the piston and undue strain on the prime mover due to the compression and expansion of fluid in the cylinder. Also to be noted here is that the unloader design minimizes the need for external piping and also reduces to a minimum the external protuberances on the compressor by providing a reverse flow-path within the compressor housing and by mounting the bypass valves I4 and I5 in the compressor housing.

While I have shown and described a specific form of my invention it is to be understood that various changes and modications may be made without departing from the spirit of the invention as set forth in the appended claims.

I claim:

1. An unloader for a multi-stage compressor having a plurality of cylinders connected in series and inlets and outlets and clearance pockets for the cylinders, comprising means for communicating the clearance pockets with the inlet of the associated cylinder for all stages but the initial stage, means for communicating the inlet with the outlet of the initial stage, valves for controlling` the communication established by the iirst said means, and-a valve for controlling the communication established by the second said means.

2. In a multi-stage compressor comprising a high pressure stage and a low pressure stage, a high pressure cylinder having an inlet and an outlet, clearance pockets for the high pressure cylinder, means for communicating the clearance pockets with the inlet, valve means for controlling said communication between the clearance pockets and the inlet of the high pressure stage, a low pressure cylinder having an inlet and an outlet, said outlet being in communication with the inlet of said high pressure stage, means for communicating the low pressure stage outlet with its inlet, and means for controlling the communication established by the last said means.

3. In a multi-stage compressor comprising a high and low pressure stage, a cylinder for the high pressure stage having an inlet and an outlet for pressure fluid, clearance pockets for said cylinder, valve means for controlling communication between said cylinder and the clearance pockets, means for communicating the inlet with said clearance pockets, valve means acting in timed relation with the action of the rst said valve means for controlling communication between the clearance pockets and the inlet, a cylinder for the low pressure stage, an inlet and an outlet for the low pressure cylinder, said outlet being in communication with the inlet of the high pressure stage, and valve means acting in timed relation with the second said valve means for controlling communication between the inlet and the outlet of the low pressure stage.

4. In a multi-stage compressor having high and low pressure stages, a cylinder for the high pressure stage defining a compression chamber, a housing for said cylinder and having members cooperating therewith to form clearance pockets and an inlet and an outlet for the cylinder, ports in the cylinder for communicating the clearance pockets with the compression chamber, unloader valves for controlling the iiow of pressure iiuid through said ports, means for controlling the operation for said unloader valves, means for communicating the clearance pockets with said inlet passage, a by-pass valve in the housing for controlling communication between the inlet passage and the clearance pockets, a cylinder for the low pressure stage, a housing for the low pressure cylinder and having members cooperating therewith to form an inlet and an outlet for the low pressure cylinder and a passage that communicates the last said inlet and outlet, an intercooler connected between the outlet passage of the low pres sure stage and the inlet passage of the high pressure stage, and a by-pass Valve in the housing of the low pressure stage for controlling the flow of pressure fluid through the passage between the inlet and outlet thereof.

5. In a multi-stage compressor having high and low pressure stages, a cylinder for the high pressure stage, a housing for said cylinder, members cooperating with said cylinder and housing to form clearance pockets and an inlet and an outlet passage for the cylinder, unloader valves for controlling communication between the cylinder and the clearance pockets, means for controlling the operation of said unloader valves, ports in some of said members for communicating the inlet and the clearance pockets, by-pass valves in the housing for controlling the ilow of iiuid through said ports, a cylinder for the low pressure stage, a housing for the low pressure cylinder and cooperating therewith to form an inlet and an outlet for the low pressure cylinder and a passage between the last said inlet and outlet, a by-pass Valve in the housing of the low pressure stage for controlling the flow of fluid through said passage between the inlet and outlet thereof, and means for controlling the last said by-pass Valve.

CHESTER W. METZGAR.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 685,704 Wilkinson Oct. 29, 1901 1,614,143 Metzgar Jan. 11, 1927 1,636,439 Resner July 19, 1927 1,969,076 Hirsch Aug. '7, 1934 

